The present embodiments relate to radio frequency identification (RFID) circuitry and, more particularly, to a dual frequency RFID circuit.
Radio frequency identification (RFID) circuits or transponders are prevalent in business, personal, and other applications, and as a result the technology for such devices continues to advance in various areas. Numerous applications for RFID circuits include automatic vehicle identification (AVI) for toll booth systems, smart card systems, book identification for libraries, pet identification systems, and inventory control. All of these systems include an interrogator and a single frequency RFID transponder. The interrogator must activate the transponder within a certain range, interrogate the transponder for specific information, and acknowledge receipt of the information. There are several advantages of the RFID circuit. First, it does not require an optical link. Thus, it can be implanted for pet identification or in a person to provide medical information. Second, it is typically powered by a received continuous wave (CW) signal from the interrogator and is, therefore, virtually maintenance free. Finally, the RFID transponder preferably communicates with the interrogator by backscattering. The transponder operates in resonance with the interrogator, modulates the original CW transmission, and sends it back to the interrogator. Thus, the RFID transponder emits no radio frequency signals until it is within range of a corresponding interrogator.
Referring to FIG. 2, there is an exemplary single frequency RFID system of the prior art which may be used for inventory control in a retail store. A detailed specification of such an RFID system is described at “EPC™ Radio-Frequency Identity Protocols, Class-1 Generation-2 UHF RFID,” Version 1.0.9, January 2005, and incorporated herein by reference in its entirety. Interrogator 200 and antenna 202 originate a single frequency CW signal to activate a pallet transponder (Pt) 206 when the pallet 210 passes through a loading dock within range of the interrogator. Separate item transponders (It) 208 are required for each item 208 on the pallet 210. These separate item transponders 208 respond to different CW frequencies from the pallet transponder 206. They are preferably activated by different interrogators at point of sale terminals. Interrogator 200 and the point or sale terminal interrogators are coupled to a central computer which collects information for each item entering or leaving the store.
While the preceding approach is a significant improvement over previous inventory control methods, the present inventor recognizes that still further improvements may be made by addressing some of the drawbacks of the prior art. In particular, there is a need to improve communication with various interrogators over different frequencies with a single RFID transponder. Furthermore, such a multiple frequency transponder must remain simple and relatively inexpensive in order to be compatible with a wide range of applications. Accordingly, the preferred embodiments described below are directed toward these benefits as well as improving upon the prior art.